Maternal health concerns are an important but understudied aspect of programs designed to prevent mother-to-child HIV-1 transmission (MTCT) in the developing world. Two of the most important and urgent questions regarding maternal health in this context are 1) whether breastfeeding by HIV-infected women is associated with excess maternal morbidity and mortality, and 2) the response to nevirapine (NVP)-containing combination antiretroviral therapy (ART) among women who have previously taken single-dose NVP for the prevention of MTCT, given the frequent emergence of drug resistant HIV-1 after single-dose NVP. HIV-infected mothers are currently being enrolled in a NICHD-funded randomized clinical trial in Botswana that is studying strategies for MTCT prevention. Women are randomized to either perinatal prophylaxis with short course zidovudine + single-dose NVP or to zidovudine alone, and to either breastfeed while giving their infant prophylactic zidovudine or to formula-feed. Women with AIDS in this study will be offered the Government ART program first-line NVP-containing ART regimen. The primary objectives of this proposal are: 1.To examine the association between randomized infant feeding strategy (breast- versus formula feeding) and time to maternal AIDS or death, and 2. To assess the proportion of women with virologic response (plasma HIV-1 RNA < 400 copies / mL) at 52 weeks after initiating NVP-containing ART among women who previously received single-dose NVP versus placebo during labor. Secondary objectives include elucidation of the etiology of possible excess maternal morbidity and mortality associated with breastfeeding by HIV-infected mothers, including micronutrient deficiency; the emergence of genotypic resistance and virologic failure in women who previously received single-dose NVP versus placebo during labor; and the tolerability and safety of and adherence to ART among pregnant and postpartum women in Botswana. This already-existing cohort with access to ART provides a unique opportunity to answer questions that have significant public health implications with a relatively small investment of additional resources.